Edge bending is an essential technique for the manufacture of automobiles, particularly their bonnets or hoods. A typical example of such hoods is shown in top plan in FIG. 14 hereof. The example hood has a cross section as shown in FIG. 15 hereof.
As shown in FIG. 14, the hood 100 includes a stiffener member 101 covered with a skin member 102, and edges of the skin member 102 are folded back around edges of the stiffener member 101 so that the skin member 102 and stiffener member 101 are secured with each other into an integral unit.
Discussion will be made next as to typical steps in a conventional method of manufacture of the hood 100 with reference to (a) to (c) of FIG. 16 hereof.
In a first step shown in section (a) of FIG. 16, there are first provided a skin member 102 having been formed by bending or drawing a blank into a predetermined shape and then bending edges 103 and 104 about 90 degrees, and a stiffener member 101 similarly formed by bending or drawing. Then, the stiffener 101 turned upside down is placed on the skin member 102 also held upside down.
In the next step shown in section (b) of FIG. 16, the edges 103 and 104 of the skin member 102 are bent inwardly; the edge bending is also called “hemming”.
Section (c) of FIG. 16 shows the hood 100 having undergone the edge bending or hemming operations. Turning this hood 100 upside down can provide the hood 100 of FIG. 15.
As examples of the hemming technique, there are known an “entire-peripheral-edge bending apparatus” disclosed in Japanese Utility Model Laid-Open Publication No. HEI-4-134225 ({circle around (1)} publication) and an “entire-peripheral-edge hemming method for a panel having a line” disclosed in Japanese Patent Laid-Open Publication No. HEI-4-351227 ({circle around (2)} publication).
In FIG. 3 of the {circle around (1)} publication, a peripheral flange portion 2a (the same reference numerals as appearing in the above-mentioned publications are used here for convenience of description of the background art) is bent, by a pre-hemming punch 18 movable in a left-and-right direction of the figure, to cover an end edge portion 3a. 
In the {circle around (2)} publication, as shown in FIGS. 3 to 5 thereof, a pre-hemming punch 9 is pivotally mounted on a pivot shaft 11, and a flange portion 2a of an outer panel is bent by moving a cam-driver punch 15 downward to thereby cause the pre-hemming punch 9 to pivot about the pivot shaft 11.
With the hemming technique disclosed in the {circle around (1)} publication, there has to be provided a means for pushing the pre-hemming punch 18 in the horizontal direction. Generally, the pushing means converts a vertical operating force of a cam-driver punch moving downward, similarly to the cam-driver punch 15 in the {circle around (2)} publication, into a horizontal force via a pivot member and cam.
However, as evident from FIG. 4 in the {circle around (2)} publication, the operating force conversion requires a plurality of intermediary component parts. Further, with the hemming technique disclosed in the {circle around (2)} publication, the pivot shaft 11 wears with long time use, as a result of which too much looseness or play would be produced between the component parts. Thus, the pre-hemming punch 9 tends to be positioned inaccurately, which would adversely affect the finishing accuracy of products.